Flow rate control valve system

ABSTRACT

A flow rate control valve system in which a valve plug is linearly driven against a valve seat by a stepping motor. The valve plug is fixed to a sleeve that has internal threads mating with external threads on the motor shaft. Splines prevent rotation of sleeve and plug. Two closely fitted cylinders are respectively supported by the motor housing and the valve plug.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a flow rate control valve system forcontrolling the flow rate by controlling the valve plug position byconverting the rotation of a stepping motor into a linear movement.

2. Background of the Invention

A flow rate control valve system of the sort disclosed by, for instanceJapanese Patent Application (OPI) No. 194658/84 is constructed so that avalve plug is fixed to the front end of the output shaft of a steppingmotor contained in a mechanism for converting its rotation into a linearmovement. Alternately, such a mechanism for converting the rotation of astepping motor into a linear movement is provided by screwing andfitting the externally threaded linear output shaft, which is allowed tomove only in the axial direction, into the threaded hollow rotary shaftof the stepping motor. When the mechanism is utilized to drive the flowcontrol valve, the front end of the linear output shaft is fixed to thevalve plug and the output shaft is moved in the axial directionproportionally to the amount of rotation of the stepping motor tocontrol the flow rate by controlling the position of the valve plugrelative to the valve seat.

An example of the latter structure is disclosed by Kobayashi et al inU.S. Pat. No. 4,381,747. In this structure, the output shaft of thestepping motor is fixed to the valve plug and is prevented from rotatingby an arm affixed to the output shaft and sliding in an axial slot ofthe motor housing. The output shaft is threaded externally to internalthreads of the motor rotor. Thereby, the turning rotor axially moves theoutput shaft. However, there results a long projection of the outputshaft.

Since the rotary shaft of the stepping motor thus constructed holds theoutput shaft linearly moving therein, the diameter of the rotary shafttends to become large and thus bearings for bearing the housing tends tobecome large and costly. Moreover, the output shaft must also pivotallybe supported and this makes the construction of the bearings for bearingboth shafts within the housing not only complicated but also large. Inaddition to the above problem, the total weight of the portions linearlydriven and the inertia increase because the valve plug and the outputshaft are linearly moved together when the valve plug is driven by theoutput shaft, thus making it extremely difficult to implement highly -responsive, high-speed and accurate flow rate control.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a smallermechanism for converting rotary motion to linear motion in a flow ratecontrol valve system.

In the flow rate control valve system according to the presentinvention, only the rotary shaft of the stepping motor is projected fromthe housing and only the valve plug is moved in the axial direction byscrewing and fitting only the valve plug allowed to move in the axialdirection into the projection. Moreover, a cylindrical body fixed to thestepping motor housing in such a manner as to enclose the portion thusscrewed an fitted therein is superposed on another portion supported bythe valve plug with a very small gap therebetween.

Since the mechanism for converting the rotation into a linear movementaccording to the present invention is realized by screwing and fittingthe valve plug into the rotary shaft of the stepping motor on theoutside thereof, it is only necessary for the bearings of the motor tobear its own rotary shaft. Accordingly, the mechanism is made simple andcompact, and highly-responsive flow control become possible because notonly the portion linearly driven but also the inertia can be reduced.Moreover, each cylindrical body superposed on the other and encirclingthe fitted portion prevents foreign substances, such as wall dustcontained in a fluid, from intruding into the contacting faces of thevalve plug and the rotary shaft even though the valve plug moveslinearly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of the sleeve portion of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, an embodiment of the presentinvention will be discribed. In FIG. 1, there is shown a stepping motor1, which is constructed as follows. A rotor 2 consists of a cylindricalpermanent magnet 3 alternately magnetized in opposed directions on itscircumference and a holding member 3a molded to fix the permanent magnet3 to a rotary shaft 4. The rotary shaft 4 is supported by an innerhousing 7 and an outer housing 8 through bearings 5 and 6 with one endof the rotary shaft 4 passing through the inner housing 7 and projectingtherefrom. The inner housing 7 is cylindrical and has a depressed end,whereas the roughly cylindrical outer housing 8 is fitted into the innerhousing 7 and is fixed in such a manner as to close the open end of theouter housing 8. A spring 9 is provided in the axial gap between theouter bearing 6 and the outer housing 8 to define the axial position ofthe rotary shaft 4 by pressing and causing the rotor 2 to be biased inthe inner axial direction through the outer bearing 6.

A stator 10 having stator coils 11 and 12, edge face yokes 13 and 14 andintermediate yokes 15 and 16 is contained in the inner housing 7. Eachof the edge face and intermediate yokes 13-16 has a pole shoe projectingin the axial direction on the inner periphery of the coil. The yokes13-16 are so arranged as to engage with each other alternately throughthe gap. A pair of combinations of the intermediate and edge face yokes13-16 and the stator coils 11 and 12 are arranged in the axialdirection. The coils 11 and 12 are wound on bobbins 17 and 18 andfurther impregnated with plastic into respective integral bodies 19 and20. The ends (including intermediate taps) of the coils are led out byleads 23 and 24 through terminals 21 and 22. The leads 23 and 24 areallowed to pass through a rubber packing 25 arranged in the outerhousing 8.

A valve system 26 that is driven in the axial direction as the rotaryshaft 4 rotates is constructed as follows. A positive screw 4a is formedon part of the outer periphery of the rotary shaft 4 projecting from thehousing 7. A sleeve 27 has a negative internal screw 27a at its rear endengaging with the positive screw 4a. The sleeve 7 includes projections27b formed on its outer periphery and projecting outside the main sleevediameter, as shown in FIG. 2. A valve plug 28 arranged at the front endof the rotary shaft 4 has an axial hole 28a into which the rotary shaft4 is fitted. The valve plug 28 is fitted into a forward end of acylindrical holder 29, which at its rear end is formed by aluminummolding to hold one end of the sleeve 27 and is incorporated into thesleeve 27 by caulking. A cylindrical self-lubricating metal guide 30prepared by impregnating sintered alloy with lubricating oil and whichis press-fitted into the axial hole 28a of the valve plug 28 tightlyholds the front end of the rotary shaft 4 and causes the valve plug 28to move linearly without toppling on the rotary shaft.

A holder 31 has concentric, axially inner and outer cylindrical members31a and 31b fixed to and held by the inner motor housing 7. The sleeve27 is fitted over the inner periphery of the inner cylindrical member31a, and there is further formed outwardly extending guide grooves 31cin the inner surface of the inner cylindrical member 31. These guidegrooves 31 mates with the projections 27b of the sleeve and extends inthe axial direction, whereby they constitute a spline mechanism with theprojection 27b operating as keys and the guide grooves 31c operating askeyways. As shown in FIG. 2, there are four pairs of mating guidegrooves 31c and projections 27b.

The length of the inner cylindrical member 31a is set great enough toprevent the projections 27b of the sleeve from being exposed even if thevalve plug 28 is moved up to maximum projected position. A spring 32 isused to press the valve plug 28 to the right of FIG. 1 and a cylindricalspring guide 33 installed concentrically about the outer periphery ofthe spring and moves together with the valve plug 28. One end of thespring guide 33 is pressed by the spring 32 against the valve plug 28and held thereby. The spring guide 33 is superposed internally of theouter cylindrical member 31b with a very small gap left therebetween toprevent foreign substances from intruding in between the interiorcontacting faces. The axial dimensions of the superposed outercylindrical member 31b and the spring guide 33 are set greater than themaximum amount of the movement of the valve plug 28 and the superposedstate is held even if the valve plug 28 moves up to the maximumprojected position. A passage housing 34 has formed therein a channel 35for fluid whose flow rate is controlled by the plug 28. The controlledchannel 35 operates as a bypass around a throttle valve in an intakepipe of the throttle valve apparatus of an internal combustion engine.The housing 7 of the stepping motor is fixed to the passage housing 34with a screw 36 and the valve plug 28 is so arranged as to face a valveseat 37 formed in the fluid channel 35.

In the embodiment thus arranged, the pole shoes of the yokes 13-16 havealternately reversed directions of magnetism and the magnetic field isswitched in predetermined order when a pulse driving signal is appliedby an external controller (not shown) to each phase of each of the coils11 and 12 in predetermined order through the terminals 21 and 22. Theyokes 13-16 are attracted and repulsed by the permanent magnet 3 of therotor, so that the rotor 2 rotates in steps according to the applieddriving signal. When the rotary shaft 4 rotates as the rotor 2 rotates,the sleeve 27 screwed into the rotary shaft 4 and splined by the innercylindrical member 31a is directly and linearly moved in the axialdirection along the guide groove 31c together with the valve plug 28. Inconsequence, the valve plug 28 changes its position relative to thevalve seat 37 according to the pulse driving signal supplied to eachphase of each of the coils 11 and 12 and is caused to control the fluidvolume in the fluid channel 35 and thus the flow rate. When the fluidchannel 35 is arranged in the bypass of the throttle valve of theengine, the valve plug 28 controls idling rotation rate by controllingthe intake amount.

To convert the rotation of the stepping motor 1 into a linear movementaccording to the present embodiment, the rotary shaft 4 projects fromthe inner motor housing 7 and the rotary shaft 4 is screwed and fittedinto the sleeve 27 incorporating the valve plug 28. Consequently, it isonly necessary to pivotally support the rotary shaft of the rotor withinthe housing 7 and 8 of the stepping motor. The thus simplified, compactconstruction of the bearing is capable of making the rotor compact andlightweight, whereas the linearly moving parts are limited to the valveplug 28 covered with the sleeve 27. Thereby, the output shaft 4extending from the inside of the stepping motor to the outside thereofneed not be moved simultaneously and linearly. It becomes possible,accordingly, to make that portion lightweight and providehighly-responsive flow rate control by reducing the inertia. Since thevalve plug 28 has an axial hole 28a in which the rotary shaft 4 isrotatably supported by the self-lubricating metal guide 30, the valveplug 28 is linearly movable without toppling on the rotary shaft and isaccurately controllable in terms of the position relative to the valveseat and therefore the flow rate. Since the spring guide 33 forming onecover member held by the valve plug 28 is superposed with the outercylindrical member 31b forming another cover member of the holder 31with a very small gap left therebetween in the radial direction, theyencircle each interior contact face even if the valve plug 28 moves backand forth and prevent foreign substances such as dust contained in thefluid from intruding therein and from causing contact failure because ofthe foreign substances. Although the sleeve 27 slides in the axialdirection while mating with the spline means provided on the innerperiphery of the inner cylindrical member 31a of the holder 31, dusthardly attaches to the contacting face on the outer periphery of thesleeve 27 because the inner cylindrical member 31a is set long enough toprevent the sleeve 27 from being exposed at the maximum position ofmovement of the sleeve (the maximum position of projection of the valveplug 28). Dust is prevented from attaching to the outer peripheralcontact face of the sleeve 27 and, in view of this, contact failure isprevented. In addition, the dust existing in the fluid is hardly allowedto intrude in between the contacting faces because the outer peripheryof the holder 29 coupling together the sleeve 27 and the valve plug 28is stepped with the constriction between the outer periphery thereof andthe edge face of the inner cylindrical member 31a of the holder 31.

By preventing the dust contained in a fluid from intruding into andattaching to the rotary-to-linear conversion means outside the steppingmotor and the contacting faces of the valve plug 28 and the linearlymoving portion, accordingly, the position of the valve plug 28 becomesstably controllable.

The disclosure of this application is similar to that of Japanese PatentApplication 60-259177, for which there corresponds U.S. PatentApplication, Ser. No. 931,827, filed Nov. 18, 1986.

As set forth above, the rotation of the stepping motor is converted intoa linear movement by screwing and fitting the valve plug onto theoutside of the projection of the rotary shaft thereof through thesleeve, whereby the axial construction of the stepping motor is suchthat it is required to support only its rotary shaft and therefore theflow rate control valve can be made simple, compact and lightweight.Moreover, since the portion that is linearly driven does not require along output shaft as in the case of the conventional valve, it is formedwith only the valve plug and thus made lightweight. Thereby flow ratecontrol with high response efficiency becomes possible. Furthermore, thecylindrical spring guide on cover member 33 supported by the valve plugand superposed on the cylindrical member on cover member 31b held by thestep motor housing with a very small radial gap left therebetween andhave overlapping ends as to encircle the contacting faces to effectivelyprevent dust contained in the fluid from intruding in between thecontacting faces and attaching thereto, so that the position of thevalve plug is stably controllable.

What is claimed is:
 1. A flow rate control valve system, comprising:amotor included within a housing and including a rotary shaft projectingfrom said housing, said projecting shaft including a screw portion on anouter circumference; a sleeve including a screw portion on an innercircumference mating with said screw portion of said projecting shaft;means for preventing a rotation of said sleeve and allowing a movementof said sleeve along an axial direction of said projecting shaft; afluid flow channel; a plug fixed to said sleeve and operative with saidfluid flow channel for controlling a flow rate of a fluid in saidchannel, said plug being fitted over an outer end of said projectingshaft; a first cylindrical cover member supported by said plug for axialmovement therewith; and a second cylindrical cover member fixablysupported by said motor housing concentric with and closely adjacentsaid first cylindrical cover member to prevent dust entry between saidcover members, and wherein said concentric first and second cylindricalcover members are of sufficient length so that ends of said covermembers are overlapped when said plug is axially projected on saidrotary shaft to the maximum extent thereof.
 2. A valve system as recitedin claim 1, wherein said motor is a stepping motor and said fluid flowchannel includes a valve seat into which said plug is movable along saidaxial direction.
 3. A valve system as recited in claim 2, wherein saidpreventing and allowing means comprises splining means connected betweensaid sleeve and said housing.
 4. A valve system as recited in claim 3,further comprising a compression spring operating against said motorhousing and biasing said first cylindrical cover member against saidplug.